Every season the Heidke skill score is high, they did well. Here's an example http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards...
How about applying some statistics, like the probability that a correct forecast (whatever that is) could be accounted for by chance, given the population of forecasts and conditions in which it takes place? P-values have their limitations, but that's no reason to discard them entirely.